A practitioner, for example a radiologist, a surgeon, or other practitioner, may use geometric quantities, for example a length of a bone, an angle of a scoliosis, or other element, in order to establish a diagnosis.
It is a known practice to take a radiograph of the osteo-articular system of a patient and to measure geometric quantities on the obtained image.
However, the value measured is marred by errors caused by the process of projection of the rays on the plane of the sensor. This error is capable of varying depending on the position of the patient in the frame of reference of the imaging installation.